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Treating aluminium for wet spray painting

Hi I wonder if you could help me. We manufacture outdoor lighting products in SA. We do not have powdercoating facilities and do a wet spray finish on our aluminium pole systems. Adhesion and corrosion are two problems that we want to combat and therefore any suggestions as to improve our painting technique are very welcome.
Sincerely,

Arno Horjus
Product designer and manufacturer - South Africa
October 5, 2009

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Hi, Arno. You haven't told us about your pretreatment, so it's hard to suggest how to improve it. But aluminum requires pretreatment, and chromate conversion coating is generally best. Can you immerse these components or do you need a wipe-on pretreatment sequence?

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
October 5, 2009

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October 6, 2009

Ted is correct in that, without detailed information on your current process, you leave us only to guess a workable process to help you. Do you bake the wet coat?
Ted if they can't afford a powder plant they will not be able to afford chromate. My suggestion would be apply a coat of ONE PACK wash/etch primer. This can be followed up using an air drying or stoving paint.
Etch primer: must be "one pack" type as this contains chromate for slowing down corrosion and phosphoric acid in the thinner/catalyst portion of the mixed system to improve adhesion. Mix sufficient for one day only... no good after 10 hours as it gel's... but this is norm. Etch primer was the mainstay of the liquid coating industry from about 1940- late 90's and still many users today. Developed by US Navy, Unfortunately It is low flash and the chromate is a health problem... however, a very good product if you do not have any other facilities.

Terry Hickling
Birmingham, United Kingdom

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I don't know if this info would help you, we are painting Al pieces with a Sherwin Williams. This three paint process uses a primer named Industrial Wash Primer.
And it work good.

Kuznetsov
- H. Matamoros, Tamaulipas, Mexico
October 8, 2009

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October 23, 2009

Thanks Kuznetsov for your input confirming my suggestion to the question for a suitable primer for aluminium items. Wash primer and etch primer are identical materials using similar resins, pigments and solvents, etc. Unfortunately, reviewing my input I stated it must be a "one pack" typeJ of course that was wrong it should be "two-pack" i.e. primer and catalystJ the rest of my input was correct.
One pack came much later, developed as dipping and high flash versions of the two etch/wash primerJ but they were never as good as the two pack version.

Terry Hickling
Birmingham, United Kingdom

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October 29, 2009

Absolutely Mr. Hickling you are completely correct.
And it was my error said three step process.. I didn't explain properly.. We are using this product from Sherwin Williams (and it comes as two compounds: the acid and the catalyzer), then we apply a epoxy primer and the top coat of polyurethane. This process provides us a very acceptable 2,000 salt fog spray hours.
My comment was because sometimes the people are asking of very specific products to their needs.

Victor Kuznetsov
- H. Matamoros, Tamaulipas, Mexico